Aqueous cleaners, including alkaline cleaners or concentrated soap solutions which typically operate at 10% strength, are known to be effective in removing oil, grease, soils and other contaminants from manufactured or processed parts, e.g., a machine component or a printed circuit board. Such cleaners are being used with increasing frequency as replacements for the ozone depleting chlorofluorocarbons (CFCs). However, the dispersants, wetting agents, and additives that are a normal part of an aqueous cleaner solution can cause severe upsets in conventional waste treatment operations, and methods of handling such cleaners without creating a wastewater treatment problem are needed.
In a typical wash process a rack mounted component is rinsed with aqueous cleaner solution, washed with fresh cleaner, and then rinsed with water in a cascade series of rinse tanks. In this process a certain amount of cleaner and associated contaminants, called the "dragout," are carried over into the rinse tanks to contaminate the rinse water. Alternatively, smaller components can be washed in tumbling barrels, then allowed to drain in a dragout tank and finally rinsed in a cascade operation. This second process produces a large amount of dragout and is typically the cause of high cleaner consumption.
Some of the waste products that can accumulate in aqueous cleaner solutions are metals and other particulate materials (including lead, flux and rosin) as well as greases and oils. As a way of handling such wastes, wetting agents and other surfactants are included in aqueous cleaner solutions to emulsify the oils, while dispersants are added to retain particulate matter in solution. In time, however, the effectiveness of the added surfactants and dispersants is exceeded; particulate matter precipitates out of solution, contaminating the crevices of a component being cleaned; and a floating oil film appears on the surface of the bath to coat articles removed from the wash tank. When conditions in the wash bath reach this level, the cleaner is spent and must be discarded although titration of the actual cleaner strength shows that the cleaner still has functional capacity.